The octet rule is not valid for the molecule

Options

A. `CO_(2)`
B. `C Cl_(4)`
C. `O_(2)`
D. `BeCl_(2)`

Answer

To determine which molecule does not follow the octet rule, we will analyze the given options step by step by drawing their Lewis structures and checking if the central atom satisfies the octet rule.

### Step 1: Analyze CO2 (Carbon Dioxide)
1. **Count the Valence Electrons:**
- Carbon (C) has 4 valence electrons.
- Each Oxygen (O) has 6 valence electrons, and there are 2 Oxygens: \(6 \times 2 = 12\).
- Total valence electrons = \(4 + 12 = 16\).

2. **Draw the Lewis Structure:**
- Carbon is the central atom (less electronegative).
- Place Oxygens on either side of Carbon.
- Form single bonds between Carbon and each Oxygen, using 4 electrons (2 for each bond).
- Distribute the remaining 12 electrons to satisfy the octet of Oxygen first.
- After distributing, form double bonds between Carbon and each Oxygen to complete the octet for Carbon.

3. **Check the Octet:**
- Each Oxygen has 8 electrons (octet satisfied).
- Carbon also has 8 electrons (octet satisfied).

**Conclusion:** The octet rule is valid for CO2.

### Step 2: Analyze CCl4 (Carbon Tetrachloride)
1. **Count the Valence Electrons:**
- Carbon (C) has 4 valence electrons.
- Each Chlorine (Cl) has 7 valence electrons, and there are 4 Chlorines: \(7 \times 4 = 28\).
- Total valence electrons = \(4 + 28 = 32\).

2. **Draw the Lewis Structure:**
- Carbon is the central atom with 4 Chlorines surrounding it.
- Form single bonds between Carbon and each Chlorine, using 8 electrons (2 for each bond).
- Distribute the remaining 24 electrons to satisfy the octet of Chlorine.

3. **Check the Octet:**
- Each Chlorine has 8 electrons (octet satisfied).
- Carbon also has 8 electrons (octet satisfied).

**Conclusion:** The octet rule is valid for CCl4.

### Step 3: Analyze O2 (Oxygen)
1. **Count the Valence Electrons:**
- Each Oxygen (O) has 6 valence electrons, and there are 2 Oxygens: \(6 \times 2 = 12\).
- Total valence electrons = 12.

2. **Draw the Lewis Structure:**
- Form a double bond between the two Oxygens, using 4 electrons.
- Distribute the remaining 8 electrons to satisfy the octet.

3. **Check the Octet:**
- Each Oxygen has 8 electrons (octet satisfied).

**Conclusion:** The octet rule is valid for O2.

### Step 4: Analyze BeCl2 (Beryllium Dichloride)
1. **Count the Valence Electrons:**
- Beryllium (Be) has 2 valence electrons.
- Each Chlorine (Cl) has 7 valence electrons, and there are 2 Chlorines: \(7 \times 2 = 14\).
- Total valence electrons = \(2 + 14 = 16\).

2. **Draw the Lewis Structure:**
- Beryllium is the central atom with 2 Chlorines on either side.
- Form single bonds between Beryllium and each Chlorine, using 4 electrons (2 for each bond).
- Distribute the remaining 12 electrons to satisfy the octet of Chlorine.

3. **Check the Octet:**
- Each Chlorine has 8 electrons (octet satisfied).
- Beryllium, however, only has 4 electrons (octet not satisfied).

**Conclusion:** The octet rule is **not valid** for BeCl2.

### Final Answer:
The molecule for which the octet rule is not valid is **BeCl2**.